Civil Engineering Reference
In-Depth Information
Fig. 13.8
The Pentagon in Washington in a perspective view and as a satellite image after the
attack (from [
11
]). The building complex is over 280 m wide and is therefore a “linear”
construction
maneuverability due to descent. An approach that is too low might hit the ground in
front of the reactor building or surrounding buildings, which results in a much lower
threat potential. An approach that is too high would either graze the dome area and
possibly be deflected, which leads to a significant reduction of the resulting load and
therefore a reduction of the threat, or miss the reactor building completely. Similar
considerations are valid for a sideways flyby.
The Pentagon was also hit during the attacks in the USA on September 11, 2001,
which is a low building in comparison to the World Trade Center. This linear
complex of buildings (cf. Fig.
13.8
) with an edge length of approximately 280 m is a
much easier target to hit, however, in comparison to a punctual reactor building
with an outer diameter of approx. 66 m. For clarification, Fig.
14.1
shows the size
comparison between the dimensions of a reactor building and the aircraft models
Boeing 747, Airbus A320 and Phantom in a horizontal section as an example.
In addition to the possible approach angles the question of the possible impact
speeds has to be addressed. The acceptable speeds set by aircraft manufacturers are
about 900 km/h (
250 m/s) for relevant aircraft models. This is a value for the
optimal flight altitude however. Close to the ground these values are significantly
reduced to about 650 km/h (
¼
180 m/s). In the case of a deliberate forced crash the
possibility has to be taken into account that the attacker will attempt to reach speeds
above those that are permitted for “normal” flight. Modern aircraft have electronic
measures, however, to prevent such an extreme flight situation. It is also important
to note that at speeds that are significantly higher than the normal speed range the
reaction time for course correction is decreased and the aircraft also becomes more
difficult to steer. The attacker has a conflict of objectives: on one hand to achieve a
speed as high as possible to maximize damage, on the other hand to maximize the
accuracy by reducing the speed.
As shown in the summary of the German Federal Environment Ministry [
10
], an
upper speed limit of v
¼
630 km/h) was established for the determina-
tion of the mechanical load-time function (cf. Chap.
14
) which is used in the further
analysis under consideration of the available information and the considerations
with respect to the accuracy above.
¼
175 m/s (
¼
